The present invention relates to vehicle drivetrains and more particularly to clutches employed between an engine and transmission.
For conventional drive trains driven by an internal combustion engine and manual transmission, there is typically a cast iron flywheel and pressure plate mounted in the dry clutch assembly between the engine and transmission. In some instances, it is desirable to reduce the rotational inertia of the clutch assembly, which has been done by using a lighter material, such as aluminum for the flywheel. However, aluminum does not have the long term wear characteristics of cast iron and so this necessitates affixing a wear resistant surface to the flywheel where it contacts the clutch disc. This has been accomplished by riveting a steel plate to the face of the aluminum flywheel on the surface that contacts the clutch disc. But riveting a steel plate takes extra manufacturing steps and requires having extra parts to assemble. It is desirable to produce such a wear resistant surface in an accurate, reliable and cost effective manner without adding additional parts to be assembled.
A further requirement for a fly wheel is that, since this component operates in a dry clutch, it must have very good heat dissipation characteristics. Aluminum dissipates heat significantly better than iron and steel, and good heat dissipation is needed for superior performance in a dry clutch application.
Moreover, there is a desire to further reduce the rotational inertia of the clutch in order to improve vehicle performance. Thus, it is desirable to have clutch rotating components made out of aluminum, in order to reduce the rotational inertia of the clutch, and yet still have adequate wear resistance and heat dissipation where needed at friction interfaces.
In its embodiments, the present invention contemplates a clutch assembly for selectively coupling an engine crankshaft to a transmission input shaft. The clutch assembly includes a flywheel assembly rotationally couplable to the engine crankshaft, and a pressure plate assembly rotationally fixed to the flywheel assembly, with the pressure plate assembly including a friction member, being formed substantially of aluminum, and including a friction face, with the friction face having a friction surface, formed substantially of a ferrous metal, and with the friction surface applied to the friction member by a PTWA thermal spray process. The clutch assembly also includes a clutch disc mounted between the flywheel and the pressure plate, and rotationally couplable to the transmission input shaft.
The present invention further contemplates a method of applying a wear resistant coating to a rotating component of a vehicle clutch, the method comprising the steps of: providing the rotating component with a friction member, with the friction member being formed from aluminum and having a friction face thereon; and creating a friction surface on the friction face by applying a ferrous metal on the friction face with a PTWA thermal spray.
Accordingly, an object of the present invention is to apply a wear resistant coating to the friction surface of an aluminum pressure plate through the use of a plasma transferred wire arc (PTWA) thermal spray process.
A further object of the present invention is to apply a wear resistant coating to the friction surfaces of an aluminum flywheel through the use of a plasma transferred wire arc (PTWA) thermal spray process.
An advantage of the present invention is that an aluminum flywheel and pressure plate, coated on their wear surfaces by the PTWA process creates components that maintain a low inertia while also improving the heat dissipation characteristics. The rotating inertia of the clutch is reduced even further since the pressure plate, in addition to the flywheel, is made of aluminum.
Another advantage of the present invention is that the aluminum components, coated with a wear resistant material, are accurately and reliably produced, with minimal coating equipment down time.